Dental implants can be used in the reconstructive therapy to compensate for the loss of a tooth. They are usually inserted into the jawbone in the place of an extracted or shed tooth, in order to hold there, after a healing-in phase of approximately four to twelve weeks, a prosthetic part serving as a dental prosthesis or a crown. For this purpose, such a dental implant is usually configured as an appropriately shaped metallic body inserted into the jawbone by screwing-in, in the intended place. As a rule, the apical end of the dental implant includes a screw thread, in most cases a self-cutting screw thread, with which the dental implant is inserted into the correspondingly prepared implant bed.
To facilitate the insertion into the patient's mouth and in particular to enable a particularly extensive preparation of the prosthesis properly speaking for its being fixed on the implant already prior to the patient's treatment, for example in a dental laboratory, dental-implant systems can be of a multi-part configuration. In particular, a generally two-part construction can be provided, the dental-implant system comprising a first implant part, also referred to as the actual implant or post part, provided for being inserted into the jawbone, and in addition to this, a second implant part associated therewith, also referred to as mounting part, on which, in turn, the dental prosthetic piece provided as a prosthesis or the like can be mounted. The outer surface of the first implant part or post part is usually provided with a thread, which can be designed as a self-cutting thread or else as a not self-cutting thread. The post part is usually anchored in a correspondingly prepared implant bed of the jawbone. The construction of the thread provided in the external area of the dental implant is usually configured for a high primary stability of the arrangement and a uniform forwarding of the forces arising under the chewing load of the dental implant, into the jawbone.
Usually, a connection pin formed onto one of the implant parts, as a rule the mounting part, is provided for mechanically connecting the implant parts with each other. This pin can be pushed into a receiving channel provided in the other implant part, as a rule the post part. With regard to the choice of geometry and dimensioning, in particular of the cross-sections, the connection pin on the one hand and the receiving channel on the other hand are usually adapted to each other in such a way that mounting is relatively easy and, nevertheless, a good guidance of the components in each other and, thus, a sufficiently high mechanical stability can be achieved. The mounting part, whose upper part is usually fitted with a crown, another prothetic provision or the like in a manner known as such, can be glued together with the post part via the connection pin pushed into the receiving channel to ensure the mechanical connection. The mounting part can, however, also be pressed into the post part and fixed only via a clamping or else can additionally be fixed by cement or glue. It is, however, also usual to connect the mounting part and the post part with each other by means of a screw joint, wherein a suitable connection screw is passed through a corresponding channel in the mounting part and engages into an associated thread in the post part.
In view of the forces arising under the chewing load and the desired long service life when using such a dental implant, the mechanical stability of the arrangement under various loads is particularly important. In particular, as a rule, even a rotation or torsion between the mounting part and the post part through external forces, mostly due to the chewing load, shall be counteracted. For this purpose, usually a mechanical indexing in the form of a mechanical lock is used, or the surface pressure between the mounting part and the post part is suitably chosen. In particular, a suitable contouring of the cross-section of the connection pin on the one hand and the receiving channel associated therewith on the other hand can be provided for indexing and to avoid a rotation of the mounting part on the post part, to form the before-mentioned mechanical lock.
However, the mechanical lock between the mounting part and the post part of multi-part implant systems in the manner of an indexing does not only serve the purpose of counteracting a rotational load, but shall in particular also assist the correct insertion of the implant in the patient's mouth with high positional accuracy, keeping the treatment time as short as possible. After the insertion of the implant properly speaking, preferably after the post parts have healed in, the spatial and geometrical data of the remaining teeth (for example antagonist teeth, teeth located mesially and distally of the place of insertion), of the mucosa and of the post part or implant, or of the mounted mounting part have to be considered in such systems in order to manufacture the crown, the bridge or other prostheses. These spatial and geometrical data are needed to manufacture the crown, the bridge or the like with precise fitting and in an anatomically optimized manner.
The indexing, i.e. the determination of the possible rotational orientation between the mounting part on the one hand and the post part on the other hand is usually achieved by suitably specifying the contour of the cross-sections of the connection pin on the one hand and of the receiving channel on the other hand in the area of their connection. Usually, the outer cross-section of the connection pin and, matching said cross-section, the inner cross-section of the receiving channel associated therewith, are for that purpose each configured in a polygonal shape, in particular a hexagonal shape, in an indexing area which may extend over the entire length or else only over a section of the connection pin, viewed in longitudinal direction of the connection pin. Thus, a hexagonal connection allows six possibilities of positioning the mounting part on the post part when mounting the mounting part.
With such a configuration of the indexing area as a polygonal connection, the main design targets, namely a relatively simple mountability, on the one hand, and a relatively high accuracy of fit, on the other hand, shall be achieved. With regard to the mountability, it is in particular desired to find the correct mounting orientation easily and quickly and to avoid, at the same time, tiltings or the like, when inserting the connection pin into the receiving channel, so that the mounting part can be placed in the patient's mouth in a relatively short time and, thus, within a short treatment time. With regard to the accuracy of fit, however, it is desired to keep the rotational play between the components, i.e. between the connection pin on the one hand and the receiving channel in the post part, as small as possible in order to enable in this way a sufficiently high mechanical stability and a long service life of the implant system. However, these two design targets conflict with each other because a high accuracy of fit requires very tight tolerances of the components, so that the assembly requires a correspondingly accurate positioning of the components relative to each other, with increased danger of undesired tilting.
Therefore, the invention is based on the problem to provide a dental-implant system of the above-mentioned type which enables a particularly simple assembly in a relatively short mounting time, while keeping the accuracy of fit of the components high and the rotational play between the mounting part and the post part correspondingly small.
This task is solved according to the invention by the fact that the connection pin comprises in the indexing area at least two sections, the outer edges, viewed in the cross-section, being rounded more strongly in a first, end-side section than in a second section.
The invention starts out on the consideration that the simultaneous fulfillment of the two conflicting design targets can be achieved by creating on the connection pin individualized partial areas or sections, each of which is specifically configured for one of the design targets. In these partial areas or sections, the characteristic parameters shall suitably be chosen in view of the respective design target. In this connection, the rounding of the outer edges of the polygon is provided as the suitable parameter via which it is possible to differentiate between the above-mentioned design targets.
In fact, for reasons of production engineering, it is inevitable, when producing a polygon, that the edges are rounded to a certain extent contrary to the theoretical mathematical shape of a genuine acute angle. Depending on the requirement, the edges can be executed with high precision and in close approximation to a genuine acute angle, with relatively little rounding. An outer cross-section of the polygon designed in such a manner leads to a very high accuracy of fit when inserting the connection pin into the receiving channel associated therewith, and the rotational play is very small. However, in this case, a very precise alignment of the components to each other is necessary when joining them. By contrast, the edges of the polygon can also be executed with a relatively strong rounding. This allows certain tolerances regarding the alignment of the components to each other, but entails an increased rotational play between the components in the assembled system.
It is, therefore, possible to achieve the two before-mentioned design targets by combiningpreferably on the end-side at the indexing area of the connection pin a first section of the connection pin, specifically aiming at facilitating the assembly, with a second section of the connection pin, specifically aiming at minimizing the rotational play between the components. To facilitate the assembly and, in particular, the positioning of the components relative to each other, the first section has relatively strongly rounded outer edges and the second section, relatively slightly rounded outer edges.
Advantageous embodiments of the invention are the subject matter of the dependent claims.
In order to ensure a high mechanical stability of the system, the connection pin and in an accordingly matching manner, also the receiving channel in the other implant part are preferably designed with straight lateral faces extending substantially in parallel to the longitudinal axis of the connection pin. In order to make the assembly even easier, the connection pin is preferably designed such that in the end region of the indexing area, which is pushed into the receiving channel during assembly, its outer dimensions taper towards the free end. For this purpose, the rounded outer edges of the connection pin are advantageously designed in the first section with a conical taper towards the free end of the connection pin.
In order to particularly promote the mechanical stability of the system after mounting and to ensure in addition a certain tightness and, thus, a long service life, the connection pin includes in an advantageous development a further region which is specifically configured for that purpose. For that purpose, the connection pin is advantageously designed, in a sealing area, with a cross-section which tapers towards the free end of the connection pin, preferably in a conical manner.
In a particularly advantageous embodiment, the respective other implant part, which includes the receiving channel for the connection pin, i.e. in particular the so-called post part or implant properly speaking, is specifically designed for a particularly simple mounting, in particular for an assembly without tilting. In the manner of a construction adapted to the basic structure of the connection pin, the receiving channel advantageously includes for that purpose a channel end piece configured as a polygon socket and in front thereof, viewed in the direction of insertion of the connection pin, a channel piece whose cross-section tapers towards the channel end piece, namely, in another advantageous embodiment, in a conical manner.
In order to keep the assembly particularly simple and, furthermore, to avoid tiltings during assembly in a particularly effective manner, the channel piece has in a particularly advantageous embodiment, in the region immediately adjacent to the channel end piece, i.e. in the transition region to the channel end piece, a larger inner diameter than the inscribed circle of the polygon defined by the inner cross-section of the channel end piece. According to the conventional definition, the inscribed circle is that circle which touches each sideline of the cross-section of the polygon in one point only; that means that in case of an even-numbered symmetry of the polygon, the diameter of the inscribed circle is equal to the distance of two opposite sides from each other. As the end-side inner diameter of the channel piece is larger in comparison therewith, an abutment edge is formed in the transition region between the corners of the polygon lying thereunder, on which the connection pin of the respective other implant part can rest when the components are joined, if the rotational orientation is not completely correct.
In another advantageous embodiment, the inner diameter of the channel piece is, furthermore, in the region immediately adjacent to the channel end piece, smaller than the diameter of the circumscribed circle of the polygon defined by the inner cross-section of the channel end piece. According to the conventional definition, the circumscribed circle is that circle which passes through the corner points of the cross-section of the polygon; that means that in case of an even-numbered symmetry of the polygon, the diameter of the circumscribed circle is equal to the distance of two opposite corners from each other. As the end-side inner diameter of the channel piece is smaller in comparison therewith, the corner geometry of the polygon extends, in the transition region in the area of the corners of the polygon lying thereunder, from the channel end piece into the preferably conical transition region of the channel piece.
It is exactly by combining these geometry parameters with each other that the above-mentioned abutment edges are formed in the areas between the corners of the polygon, on which the end region of the connection pin can rest while the components are mounted, together with extensions of the corners of the polygon in the transition region. Due to the rounded end side of the outer contour of the connection pin, the latter can be rotated, while resting on the abutment edges, far enough to correct the rotational orientation without any significant risk of tilting, in a relatively unproblematic manner.
The abutment edge can be configured in a substantially level manner. In a further advantageous embodiment, however, the abutment edge formed in the contact area by the channel piece and the channel end piece is configured with a bevel. The angle of inclination of the abutment edge, in particular inwards towards the central axis of the receiving channel, is advantageously smaller than the triple, preferably smaller than the double, particularly preferably smaller than the 1.5 fold, of the cone angle in the sealing area. This ensures a reliable guidance of the connection pin during its insertion into the receiving channel.
The advantages achieved with the invention consist in particular in that the connection pin, which is configured in the indexing area with different geometry parameters in different sections, in particular with a rounding of the outer edges varying from one section to the other, makes it possible to achieve actually conflicting design targets for the overall system, namely a simple and fast mountability and, at the same time, a small rotational play. The rounding can be provided, as specified in the present case, for polygon-based systems. Of course, the rounding can also advantageously be applied in similar systems in which indexing is given by local maxima of the diameter.